Induction furnaces for melting metal by generating magnetic fields which induce eddy currents to flow within and heat the metal are well-known. In such furnaces, an induction coil assembly creates the magnetic fields. Induction coil assemblies are commonly considered to include an induction coil, and upper, lower and intermediate yokes. One such induction coil assembly is described in the already referenced U.S. patent application Ser. No. 08/019921, filed Feb. 19, 1993. The induction coil assembly of U.S. Ser. No. 08/019921, in most of its disclosed embodiments, surrounds but is separated from a crucible that holds the metal being heated. The induction coil assembly disclosed in that application comprises upper and lower yokes electromagnetically coupled together by intermediate yokes and all of such yokes cooperating with a helical induction coil that is wrapped around the crucible.
Because of the high power typically required to accomplish industrial-scale heating of the metal within the crucible, the induction coil assembly and its components are relatively large. A relatively large induction coil assembly is well-suited to its desired purpose, but its size becomes a disadvantage in the event of a fault condition. More particularly, if the induction coil assembly experiences a fault, an inordinate amount of time is typically required to disconnect and then reconnect the faulty component of the assembly, as well as the relatively large cables associated with delivering the high power to these components. The excessive disconnect and reconnect times directly contribute to excessive down time in which the associated induction furnace is removed from production.
An induction furnace having a replaceable coil assembly which facilitates its removal and replacement is known and is made available from Pillar Industries Limited Partnership of Menomonee Falls, Wis. as their "shunt pac design." The replaceable coil assembly is a one-piece unit having so-called stud board members which are circumferentially spaced apart from each other and which physically support the induction coil of the assembly. These stud board members limit the amount of circumference of the induction coil that can be covered by the intermediate yokes, because the intermediate yokes cannot be placed about the induction coil in those regions already occupied by the supporting stud board members. This limitation restricts the amount of the circumference of the induction coil covered by the intermediate yokes to a factor of between 50 to 60% of the total circumference of the wound induction coil. It is desired that means be provided so that the amount of the circumference of the induction coil covered by the intermediate yokes is increased from this 50-60% factor to that of about 80% or better.
Induction coil assemblies having provisions to allow for access to components to facilitate replacement thereof also have a drawback in that such access allows for debris to find its way into the interior of the induction coil assembly. Usually, this debris is metallic and it is created during the formation and/or pouring of the metal heated by the furnace. This metallic debris is typically attracted to the magnetic yokes and may move around within the induction coil assembly to cause ground fault. It is desired that the entrance of the debris into the interior be restricted, while at the same time still providing provisions to easily remove any such entered debris, especially if the debris finds its way into the general region of the intermediate yokes so that any related ground faults may be quickly cleared.
In addition to providing provisions to facilitate the removal of ground faults and also the removal of induction coil assemblies themselves, it is important that the induction furnace be substantially free of operational vibration noise. Such noise commonly manifests itself as a humming sound emanating from the induction furnace, in particular from the induction coil. This noise may be of particular annoyance to the operators of the furnace, especially when subjected to it over a long period of time. It is desired that means be provided to substantially reduce the noise emanating from the induction coil.
Accordingly, it is an object of the present invention to provide an induction coil assembly that is easily removed from the induction furnace yet has an arrangement wherein the vast majority of the circumference of the wound induction coil is covered by the intermediate yokes.
It is a further object of the present invention to provide an induction coil assembly that is easily removed and has provisions to allow any unwanted metallic debris to be conveniently moved from its confines, especially from the general regions of the intermediate yokes.
Further still, it is an object of the present invention to provide an induction furnace having an induction coil assembly with a modular arrangement that facilitates easy and quick removal of some of its intermediate yokes in the event of a fault so as to increase the overall availability and production time of the induction furnace while at the same time reduce the level of noise commonly emanating from the induction coil.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.